A 33-year-old Italian engineer who has been in London since 2018 has been plunged into a battle with the Home Office after officials told him they made a mistake allowing him to stay in the UK after Brexit.

Fabio, who initially came to London to finish his doctorate and who has built a successful career working on energy and climate change, says he is shocked by the development as he has not broken any rules since Brexit.

He was given settled status under the EU settlement scheme, permanent residency given to qualifying EU citizens after five years in the UK.

The Home Office has now told him this was “in error” – and his wife, who he has been with since arriving in the UK, now has no right to remain as a qualifying family member of someone with settled status.

While officials told him he could remain in the UK as they would not be removing his settled status, despite their claim to have made a mistake, the consequence of their error is that his wife now has no right to be in the country with him.

“It was quite devastating for both of us. We have been here for a long time. We have done everything by the book, and we’ve always felt very welcome here and I always thought this is somewhere I could grow my career.

“It is so upsetting and frustrating to know that we are now in this vulnerable position just as we were thinking of building a family, buying a place for ourselves. Now all our plans must stop,” he said.

Fabio, whose name has been changed, is one of more than at least 100 individuals who have been contacted by the Home Office to say an “error” had been made in awarding them status under the EU settlement scheme.

The Home Office wrote to him in April as part of a review that appears to have been triggered by his Brazilian wife’s application for status under the EU settlement scheme.

He too was born in Brazil but is an Italian dual national by birth and provided a certificate to demonstrate this from the Italian consulate in his settled status application.

Officials have now told him the evidence of his Italian citizenship was “insufficient”, and they needed proof that he was Italian before the Brexit cut-off date of 31 December 2020.

“It has therefore been decided that, on the basis of the information and evidence currently available, your settled status under the EU settlement scheme was granted in error,” the Home Office said.

It added he was no longer “relevant EEA citizen” and he would therefore not be able to sponsor a family member, his wife, to remain in the UK.

Catherine Barnard, professor of EU law at the University of Cambridge, said she was astonished by his case, which suggested the Home Office was creating a two-tier system.

“This appears to be contrary to the withdrawal agreement on the basis of which his rights were granted. The Home Office cannot punish him by saying he has only second-class rights and, in particular, that he doesn’t have family rights so long as he retains settled status,” she said.

She points to article 13 (4) of chapter two of the EU-UK withdrawal agreement, which states “the host state may not impose any limitations or conditions for obtaining, retaining or losing residence rights”.

The Home Office has contacted at least 100 people, but possibly many more, to tell them they made “an error” in awarding status.

Monique Hawkins, acting chief executive of the3million, said stripping people of rights in such a way would affect “whole families” as people faced a “cliff-edge loss of their rights” without any of the “proportionality assessment” required under the withdrawal agreement.

The Independent Monitoring Authority, the statutory body set up to implement the EU-UK withdrawal agreement, has also said it is worried that the Home Office moves “may be incompatible with the EU withdrawal agreement”.

It has written to the Home Office to raise “discretionary decisions” about the original applications for post-Brexit residency being made by caseworkers revisiting historic decisions.

It has asked any EU citizen who is experiencing difficulties to contact them.

Mala Savjani, partner at Wilson Solicitors in London, which is acting for Fabio, said it was “not clear why” the government was “targeting EU nationals who have dual nationality”.

She added: “In order to come to its conclusions, the Home Office is having to make, sometimes unverified, assertions about complex areas of other EU member states’ nationality laws. It is not evident what the policy objective is.”

The Home Office said: “It is longstanding government policy that we do not routinely comment on individual cases.”

However, officials said the case was “not a breach of the withdrawal agreement” and “those who have been granted EU settlement scheme (EUSS) status in error are not withdrawal agreement beneficiaries and, unless they can [provide] evidence they meet the requirements for that status, have no basis of qualification under the EUSS”.